1. Field of the Invention
This invention relates to an apparatus for processing a reproduced signal in a digital recording/reproducing system or transfer system using a magnetic recording medium and, in particular, to bit identification for converting a reproduced signal into a binary signal.
2. Description of the Prior Art
In a digital recording/reproducing system or a digital transfer system, an increase in recording density invites a decrease in S/N ratio of a signal reproduced from a magnetic recording medium (magnetic tape, magnetic disk and so on), and increases such errors so that the reproduced digital signal does not correspond to the recorded digital signal. There is a need for a signal processing technique that properly detects a digital signal from an analog waveform from a reproducing head.
A known existing signal processing technique available for this purpose is an integral detecting method. This method executes equalization based on an equalizing standard, called the Nyquist standard, to minimize intersymbol interference at an identified point and then binarizes the Nyquist waveform, in view of the value relative to a predetermined threshold value.
However, it is difficult to realize an equalizer fully satisfying the equalizing standard, and the existing method has a problem that errors concentrate around the threshold value because of random noise, low range shutoff, and high range shortage, and so on, with respect to the reproduced signal.
Digital signal reproducing apparatuses using integral detection have heretofore required an automatic equalizer having a simple construction and capable of compensating variations and changes with time in characteristics of tape or heads. If a transversal filter is used, an automatic equalizing algorithm can be used, and such an equalizer can be realized. However, sufficient equalization is not possible with a small number of taps. If the number of taps is increased, a resultant circuit is large-scaled. Therefore, no automatic equalizer has been available for practical use.